Video transmission system using time-warp scrambling

Abstract

A subscriber cable television system using predominantly digital signal processing techniques employs an improved time-warp and segment scrambling method for providing extremely high security. Means are also disclosed for suppressing the undesirable effects of discontinuities in the scrambled video signal by methods of inserting additional data samples between adjacent continuous segments, and by dithering the video line positions of the discontinuities. Preferably the scrambler and descrambler each have a memory for storing video samples, first and second address counters for providing read and write addresses to the memory, and means for decrementing or inhibiting address counting during the time between segments of continuous video samples in order to insert and delete samples during scrambling and descrambling, respectively.

What is claimed is: 
     
       1. An encoder for generating a scrambled composite video signal for secure transmission, the video signal having a plurality of video lines, each video line including a video data portion, said encoder comprising the combination of: means for sampling the video data portion for each video line at a periodic rate and subdividing the video data portion for each video line into a plurality of segments,   a pseudorandom number generator for generating a plurality of pseudorandom number for at least some of said video lines, each pseudorandom number having multiple bits,   video scrambling means responsive to said pseudorandom numbers for inverting the polarity of the samples in selected segments, for reversing the order of the samples in selected segments, and for reversing the order of the segments in selected segment pairs.   
     
     
       2. An encoder as set forth in claim 1 wherein said video data portion is divided into multiple sectors of approximately equal length, each sector is subdivided into at least two segments of approximately equal length, and said video scrambling means reverses the order of segments within selected sectors. 
     
     
       3. An encoder as set forth in claim 1 which includes means for inserting an additional data sample between adjacent segments, said additional sample having the same value as that of the immediately following sample so that undesirable effects from discontinuities between adjacent segments are substantially reduced.   
     
     
       4. A video transmission system providing secure transmission of a composite video signal over a communications channel for reception by designated customers, the composite video having audio information, scrambled video information in frames having a predetermined number of lines, synchronization information indicating the first line in each frame, program data identifying the transmitted program material, and customer data for designating individual customers permitted to receive the composite video signal and descramble the video information therein, the video transmission system having an encoder as set forth in claim 1 for generating the scrambled video information from station video, and means for generating the audio information from station audio, and a decoder for each customer for receiving the composite video signal and descrambling the video signal therein in response to the customer data in the composite video signal. 
     
     
       5. A video transmission system as set forth in claim 4 wherein the communications channel comprises a coaxial cable providing low-noise transmission from the encoder to the decoders, and wherein the audio information, program data and customer data are encoded and time-multiplexed with the scrambled video information, the encoded audio information, program data and customer data being digitized in binary format, and the binary data is time-multiplexed into the composite video at a density of at least one bit approximately every 100 nanoseconds. 
     
     
       6. A video transmission system as set forth claim 4 wherein the audio information is inserted into the horizontal blanking time of the composite video signal, the program and customer data is inserted into the vertical blanking time of the composite video signal, and the composite video signal includes a signal during the horizontal blanking time of each line a predetermined time after the start of each line indicating whether the respective line is the first line in a frame. 
     
     
       7. A video transmission system as set forth in claim 6 wherein the program and customer information comprises, for each frame, a system identifier and program information. 
     
     
       8. A video transmission system as set forth in claim 4 wherein the audio information includes at least two distinct channels, and the audio information comprises at least seventy-two binary bits per line of composite video. 
     
     
       9. A video transmission system as set forth in claim 6 wherein the audio information includes at least two distinct channels, and the audio information comprises at least seventy-two binary bits per line of composite video. 
     
     
       10. A video transmission system as set forth in claim 4 wherein the audio and video information are scrambled and descrambled by a pseudorandom number generated by pseudorandom number generators in the encoder and decoder, the seed for the pseudorandom number in the decoder being specified for each frame by digital seed information encoded into the composite video signal. 
     
     
       11. A video transmission system as set forth in claim 6 wherein the audio and video information are scrambled and descrambled by a pseudorandom number generated by pseudorandom number generators in the encoder and decoder, the seed for the pseudorandom number in the decoder being specified for each frame by digital seed information encoded into the composite video signal. 
     
     
       12. A video transmission system as set for in claim 11 wherein the first line of each frame has customer, program, and seed information encoded therein comprising a system identifier, program information, and seed information. 
     
     
       13. A video transmission system as set forth in claim 4 wherein each line of the composite video signal includes a sinusoidal color burst portion, the sinusoidal color burst portion providing a decoder phase reference used as the color subcarrier phase reference for any color programming in the composite video signal, the time zero reference for each line being defined by a predetermined phase point on the decoder phase reference the time positions wherein the binary bits of the audio information and customer and program data are encoded in the lines of composite video being synchronized to the decoder phase reference at predetermined time intervals from the time zero reference. 
     
     
       14. The video transmission system as claimed in claim 13 wherein the customer and program data are correlatively encoded. 
     
     
       15. A video transmission system as set forth in claim 13 wherein the program data includes at least one bit identifying the video information as black-and-white, and the decoder comprises means for enabling color killer circuits when the program data identifies black-and-white video information. 
     
     
       16. A video transmission system as set forth in claim 4 wherein the audio information is inserted into the horizontal blanking time of the composite video signal and the program and customer data is inserted into the vertical blanking time of the composite video signal, the composite video signal including an analog sample during the horizontal blanking time of each line, a predetermined time after the start of each line, indicating whether the respective line is the first line in a frame, and wherein the audio information, program data and customer data are encoded into analog samples of the composite video signal and time-multiplexed with the scrambled video information, the encoded audio information, program data and customer data being digitized in binary format, wherein at least two binary bits of digitized, binary data are encoded into one analog sample of the composite video signal. 
     
     
       17. A video transmission system as set forth in claim 16 wherein the audio and video information are scrambled and descrambled by a pseudorandom number which generally changes at least once for each line, the pseudorandom number being generated by pseudorandom number generators in the encoder and decoder, the seed for the pseudorandom number in the decoder being specified for each frame by digital seed information encoded into the composite video signal. 
     
     
       18. A video transmission system as set forth in claim 17 wherein the first line of each frame has customer, program, and seed information encoded therein comprising a system identifier, program information, and seed information. 
     
     
       19. The video transmission system as claimed in claim 16 wherein each line of the composite video signal comprises a synchronization edge portion followed by a sinusoidal color burst portion, the sinusoidal color burst portion providing a decoder phase reference used as the color subcarrier phase reference for any color programming in the composite video signal, the time zero reference for each line being defined by a predetermined phase point on the decoder phase reference, the time positions of the analog samples in the composite video encoding the audio information and customer and program data in a line being synchronized on the decoder phase reference at predetermined time intervals from the time zero references. 
     
     
       20. A video transmission system as set forth in claim 19, wherein each line of the composite video signal includes a max reference pulse immediately following the horizontal edge portion, the max reference pulse providing a full scale signal to establish a reference for analog-to-digital conversion of the composite video signal. 
     
     
       21. A video transmission system as set forth in claim 19 wherein the program data includes at least one bit identifying the video information as black-and-white, and the decoder comprises means for enabling color killer circuits when the program data identifies black-and-white video information. 
     
     
       22. A video transmission system as set forth in claim 4 wherein each line of the composite video signal comprises a sinusoidal color burst portion providing a decoder phase reference used as the color subcarrier phase reference for any color programming in the composite video signal, the customer and program data being received in synchronism with the decoder phase reference, and wherein the program data includes at least one bit identifying the video information as black-and-white, and the decoder comprises means for enabling color killer circuits when the program data identifies black-and-white video information. 
     
     
       23. An encoder for generating a scrambled composite video signal for secure transmission, the video signal having a plurality of video lines, each video line including a video data portion, said encoder comprising the combination of: means for sampling the video data portion for each video line at a periodic rate and subdividing the video data portion for each video line into a plurality of segments, and   means for inserting additional data samples between adjacent segments, one of said additional samples having the same value as that of the last sample of one of the adjacent segments, one of said additional samples having the same value as that of the first sample of the other of the adjacent segments, and one of said additional samples having a value equal to the average of the value of the other two additional samples, so that undesirable effects from discontinuities between adjacent segments are substantially reduced.   
     
     
       24. An encoder for generating a scrambled composite video signal for secure transmission, the video signal having a plurality of video lines, each video line including a video data portion, said encoder comprising the combination of: means for sampling the video data portion for each video line at a periodic rate and subdividing the video data portion for each video line into a plurality of segments,   means for altering a major portion of said segments in a major portion of said lines in accordance with a predefined pseudorandom code containing at least five bits per segment pair,   means for inverting the polarity of a first segment in each pair in response to a first of said bits,   means for inverting the polarity of a second segment in each pair in response to a second of said bits,   means for reversing the order of the samples in a first segment in each pair in response to a third of said bits,   means for reversing the order of the samples in a second segment in each pair in response to a fourth of said bits, and   means for reversing the order of said first and second segments in each pair in response to a fifth of said bits.   
     
     
       25. A decoder for decoding a scrambled composite video signal which has been periodically sampled and comprises substantially continuous video segments separated by at least one video sample, said video signal having been scrambled by (1) inverting the polarity of the samples in selected segments, (2) reversing the order of the samples in selected segments, and (3) reversing the order of the segments in selected segment pairs, all in accordance with a predefined pseudorandom code, said decoder comprising the combination of a pseudorandom number generator for generating a plurality of pseudorandom numbers for at least some of said video lines, each pseudorandom number having multiple bits, and   video de-scrambling means responsive to said pseudorandom numbers for (1) restoring the polarity of the inverted samples in said video segments to the polarity of such samples in the original video segments, (2) restoring the order of the reversed-order samples in said video segments to the order of such samples in the original video segments, and (3) restoring the order of the reversed-order segments in said video data portion of said video lines to the order of such segments in the original video lines.   
     
     
       26. A decoder as set forth in claim 25 wherein the seed for said pseudorandom number generator in the decoder is specified for each frame by digital seed information encoded into the component video signal. 
     
     
       27. A decoder as set forth in claim 25 further comprising a memory for temporarily storing periodic samples of the scrambled composite video signal and means responsive to the predefined pseudorandom code for changing the memory address so that the time sequences of the samples in some of the video segments are altered so as to be substantially continuous as the pairs of samples are read from the memory. 
     
     
       28. A decoder as set forth in claim 27 wherein the means for changing the memory address comprises at least one exclusive-OR gate for selectively changing the segment address portion of the memory address, so that some of the segments are swapped in response to the pseudorandom code by the effect of the exclusive-OR gate. 
     
     
       29. A decoder as set forth in claim 27 wherein the means for changing the memory address comprises a bank of exclusive-OR gates for selectively complementing the lower order memory address bits specifying the time position of the samples in each segment in order to perform selectively a time inversion of some of the segments. 
     
     
       30. A decoder as set forth in claim 25 for processing a composite video signal having video information in fields having a number of lines in each field, synchronization information indicating the starting position of the lines and the first line in each frame, and a color burst portion at a predetermined position in the video lines having a number of cycles in phase with the suppressed carrier of any color information in the video information, said decoder including a system timing circuit for recovering the synchronization information despite the presence of received noise, comprising, in combination, horizontal sync threshold detector means responsive to the synchronization information in the composite video signal and indicating, to a high probability, whether the starting point of a line is present,   horizontal sync detector means for generating a horizontal sync pulse in synchronism with a sample clock immediately after the horizontal sync threshold detector means indicates the starting point of a horizontal line,   horizontal counter means clocked by the sample clock and reset by the horizontal sync pulse for identifying sample positions along each video line,   state decoder means for generating gating signals coincident with predetermined sample positions along each video line, a chroma burst gate being generated corresponding to the predetermined position of the chroma burst portion in the video lines, and   a chroma burst phase-locked loop accepting the chroma burst gate and having a reference oscillator, the phase error between the reference oscillator and the chroma burst portion being sensed when the chroma burst gate is active for locking the reference oscillator to the phase of the chroma burst portion, and having means for generating the sample clock synchronized to the reference oscillator.   
     
     
       31. A decoder as set forth in claim 30 wherein said state decoder means generates a vertical sync gate at a predetermined sample position along each video line, and further comprising vertical sync detector means for sampling the composite video signal upon the coincidence of the vertical sync gate and generating a vertical sync pulse if, to a high probability, vertical synchronization information is present, and a vertical counter reset by the vertical sync pulse and counting once for each line.   
     
     
       32. A decoder as set forth in claim 30 wherein the horizontal sync detector means has means for memorizing the frequency at which the starting points of the lines are detected, and has means for generating horizontal sync pulses at that frequency when the horizontal sync threshold detector fails to indicate the starting points of the horizontal lines. 
     
     
       33. A decoder as set forth in claim 25 wherein said horizontal sync detector means comprises, in combination, a first counter clocked at a generally constant rate and being set to a predetermined state upon the occurrence of the input horizontal sync pulses,   a second counter clocked at a generally constant rate and having means for being set to an initial state depending on the state of the first counter just before the first counter is set to the predetermined state, and   means for regenerating missing horizontal sync pulses when the second counter reaches a predetermined final state,   the first and second counters counting in opposite directions so that the regenerated horizontal sync pulses are phase locked to the input horizontal sync pulses despite varying line length.   
     
     
       34. A decoder as set forth in claim 33 wherein said horizontal sync detector further comprises means for generating a window gate when the first counter reaches a predetermined range of states setting the upper and lower bounds on the permissible horizontal period and gating means for qualifying the horizontal sync pulses when the horizontal sync pulses occur within the window gate interval and means for indicating whether a qualified horizontal sync pulse is received for each horizontal line. 
     
     
       35. A decoder as set forth in claim 34 wherein said means for setting the second counter to an initial state depending on the state of the first counter comprises a latch receiving the output of the first counter and gated by the qualified horizontal sync pulses, and means for presetting the second counter to an initial state depending on the output of the gated latch upon the occurrence of a regenerated horizontal sync pulse and also upon the occurrence of a qualified horizontal sync pulse, so that continuously missing horizontal sync pulses are regenerated, the repetition rate of the regenerated sync pulses being dependent on the value stored in the gated latch. 
     
     
       36. A decoder as set forth in claim 35 wherein said horizontal sync detector further comprises means responsive to the state of the second counter for specifying operations synchronized to the end of the horizontal line. 
     
     
       37. In a video transmission system providing secure transmission of a composite video signal over a communications channel for reception by designated customers, the composite video having scrambled video information in frames having a predetermined number of lines, synchronization information indicating the starting positions of the lines and the first line in each frame, program data identifying the transmitted program material and customer data for designating individual customers permitted to receive the composite video signal and descramble the video information therein, a decoder as set forth in claim 25 having means for detecting the synchronization information and thereupon generating horizontal sync pulses indicating the starting positions of the lines, and means for latching the customer and program data for each line, means for generating a window gate signal a predetermined time after each horizontal sync pulse, the window gate signal establishing upper and lower bounds on the permissible horizontal period, and   means for indicating a qualified horizontal sync pulse whenever one of the horizontal sync pulses is within the permissible time window set by the window gate, and means for generating a signal for gating the latches which receive the customer and program data, the gating signal enabling the latches for each horizontal line following a qualified horizontal sync pulse.   
     
     
       38. In a video transmission system providing secure transmission of a composite video signal over a communications channel for reception by designated customers, the composite video having audio information, scrambled video information in frames having a predetermined number of lines, synchronization information indicating the first line in each frame, program data indentifying the transmitted program material and customer data for designating individual customers permitted to receive the composite video signal and descramble the video information therein, a decoder as set forth in claim 25 having means for detecting the synchronization information and thereupon generating horizontal sync pulses indicating the starting positions of the lines, and an analog-to-digital converter receiving the composite video signal, the composite video signal having a max reference pulse, an analog transmission gate sampling the value of the max reference pulse, and a capacitor for holding the sampled value of the max reference pulse, and wherein the sampled value held on the capacitor establishes a reference for the analog-to-digital converter.   
     
     
       39. A video transmission system as set forth in claim 38 wherein the composite video signal has a ground reference signal at a predetermined position in each line, and wherein the decoder includes an analog transmission gate connected to a ground reference level for sampling the ground reference signal of t z composite video signal, thereby precisely clamping the composite video signal to the ground reference level. 
     
     
       40. In a video transmission system providing secure transmission of a composite video signal over a communications channel for reception by designated customers, the composite video having audio information, scrambled video information in frames having a predetermined number of lines, synchronization information indicating the starting positions of the lines and the first line in each frame, program data identifying the transmitted program material and customer data for designating individual customers permitted to receive the composite video signal and descramble the video information therein, at least a portion of the customer data for a particular customer being transmitted in a preassigned time slot in a video line including a record number preassigned to the particular customer, and the first line of each frame comprises customer, program, and seed information encoded therein, a decoder as set forth in claim 25 having means for detecting the synchronization information and thereupon generating horizontal sync pulses indicating the starting positions of the lines, and a customer memory programmed with a customer identification number including a programmed customer record number and a programmed customer time slot identifier, and means for latching the customer data from a video line having a record number matching the programmed customer record number, the customer data being lached from the video line at a time slot indicated by the programmed customer time slot identifier.   
     
     
       41. In a video transmission system providing secure transmission of a composite video signal over a communications channel for reception by designated customers, the composite video having audio information, scrambled video information in frames having a predetermined number of lines, synchronization information indicating the starting positions of the lines and the first line in each frame, program data identifying the transmitted program material and customer data for designating individual customers permitted to receive the composite video signal and descramble the video information therein, the composite video signal having horizontal sync pulses having a maximum value reduced at least approximately minus 20 IEEE units in comparison with a standard composite video signal, a decoder as set forth in claim 40 having a threshold detector having a threshold set between the level of the horizontal sync pulse and the video level for the case of a black signal, and detector means for eliminating the pulses from the threshold detector, generated by the chroma modulation in the composite video signal.   
     
     
       42. A video transmission system as set forth in claim 41 wherein the amplitude of the horizontal sync pulses is limited to the maximum permitted swing of the modulation of the video portion of the composite video signal. 
     
     
       43. In a video transmission system providing secure transmission of a composite video signal over a communications channel for reception by designated customers, the composite video having scrambled video information in frames having a predetermined number of lines, synchronization information indicating the starting positions of the lines and the first line of each frame, program data identifying the transmitted program material and customer data for designating individual customers permitted to receive the composite video signal and descramble the video information therein, the program data in the composite video signal includes a parental guidance rating number, and the customer data includes parental guidance threshold levels for particular customers, a decoder as set forth in claim 25 for a designated customer having means for detecting the synchronization information and thereupon detecting the starting positions of the lines, and means for latching the customer data for the designated customer and program data for each line, wherein the means for latching the customer and program data includes means for latching the threshold level for the designated customer, and wherein the decoder is enabled so long as the parental guidance rating of the particular program does not exceed the threshold level for the designated customer.   
     
     
       44. A video transmission system as set forth in claim 43 wherein the parental guidance number is a four bit number and wherein the parental guidance threshold level is one of sixteen levels.